Ignition coils are used for example in vehicles having a spark ignition engine to trigger a spark plug, in order to ignite a fuel mixture in a combustion chamber of the spark ignition engine. Ignition coils are constructed for example as rod ignition coils, in which a primary coil and a secondary coil are situated around a centrally located rod core of a magnetizable material. A storable magnetic energy for the ignition coil depends significantly on the design of its magnetic circuit. A known magnetic circuit is depicted in FIGS. 6a and 6b. As is apparent from FIG. 6b, this magnetic circuit has what is known as an O-I core arrangement. An inner core 10 and an outer core 11 of the magnetic circuit are each made up of a large number of plate-like leaves. The leaves of outer core 11 have an essentially O-shaped form, with a projection 11a. The leaves of outer core 11 are produced by stamping, it being necessary for reasons of production technology to maintain a certain minimum width Y. Width Y is significantly greater than thickness Z of the individual leaves (see sectional drawing 6a, which is cut along line A-A of FIG. 6b).
Because of the steadily shrinking designs of transformers and ignition coils, greater and greater demands are being made on the magnetic circuits of such components in terms of efficiency and size. Special attention must be paid to equality of cross sections and absence of air gap when magnets are used. If no magnets are employed, a defined air gap must be provided instead of the magnet. Furthermore, because of the need for overlap between the inner and the outer core, the space is inadequately utilized in the height direction (in the direction of thickness Z of the leaves stacked one above the other).